Bonding washer

ABSTRACT

A bonding washer for making electrical connection between two metal pieces that are to be mechanically fastened together. The washer, to be interposed between the two metal pieces, may be constructed so as to fasten to one of the pieces before the two pieces are joined. Teeth on the washer, positioned at right angles to the plane of the washer, are forced into each of the two metal pieces when the fastener is tightened, making electrical connection between the two metal pieces.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 13/324,688, filed Dec. 13, 2011, which is a continuation of application Ser. No. 11/308,683, filed Apr. 21, 2006 (now U.S. Pat. No. 8,092,129), both of which are incorporated by reference herein in the entirety.

FEDERALLY SPONSORED RESEARCH

Not Applicable

REFERENCE TO SEQUENCE LISTING

Not Applicable

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to construction of photovoltaic arrays and other apparatus requiring electrical connection between metal parts.

2. Prior Art

This invention has been devised for use in installing a photovoltaic array composed of a number of photovoltaic modules that are assembled onto a larger mounting structure. The frames of the individual photovoltaic modules and the structural pieces on which the modules mount are generally made out of aluminum. The aluminum is anodized to resist corrosion. As in any source of electrical power, to ensure safety the metal pieces must be bonded together. Bonded is used here in the technical sense to mean permanently joined to form an electrically conductive path that ensures electrical continuity and has the capacity to safely conduct any current likely to be imposed. Although the frames of the modules are directly bolted or clamped to the mounting pieces, the anodizing insulates the pieces so that they are not electrically connected together.

A common practice in the industry is to install a separate grounding lug on each piece that is anodized. The grounding lug is attached to the sheet metal frame of the modules with a thread forming stainless steel screw. Since the screw cuts into the aluminum it forms an air-tight connection which will maintain good electrical connection over time. A common sheet metal thickness is 0.080 inch and a common screw size is 10-32 so that the screw therefore only makes connection on about 2½ threads. This gives a marginally acceptable surface contact area in terms of mechanical strength and electrical conductivity. It would be desirable to have a design where the electrical contact area can be made much larger.

The stainless steel screw contacts a star washer which in turn contacts the grounding lug body. The grounding lug accepts a copper wire which is forced to contact the grounding lug by a stainless steel set screw. There are thus four connection points which must be made, sheet metal to screw, screw to star washer, star washer to lug, and lug to copper wire. It would be desirable to have a design where there are only two electrical connection points.

Copper wire is strung between grounding lugs on all the metal pieces and eventually to a ground electrode. The grounding lugs themselves are expensive and time consuming to install and the wiring adds both material and labor cost which increase the price of the overall system. It would be preferable if the electrical connection was made directly between the metal pieces when they are assembled together.

Star washers, such as that in FIG. 1, are generally available for making electrical connections. They are constructed so that they can be punched and formed out of flat metal stock. The forming process makes a number of internal or external teeth that are usually twisted so that they extend above and below the plane of the washer body. Star washers make electrical connection to an adjacent piece because they tend to dig in to the adjacent piece as they are rotated and compressed by a nut and bolt being tightened. In the intended application, they would be inserted in between the two pieces of metal to be bonded. They will therefore be separated from the nut and bolt by a layer of material and so will not rotate in the usual manner and therefore will be less effective. Star washers are intended for applications where all they have to break through is grease or dirt on a metal surface, but anodized aluminum is a very hard material. The teeth of a star washer will act like springs and deform back to a flat surface when compressed. This is desirable for most applications because the spring action maintains contact. In this application, however, depending on the thickness of the anodizing, the star washer may or may not penetrate the anodizing to make connection with the underlying aluminum metal. Some examples of this type construction are found in U.S. Pat. No. 5,453,027 (Buell et al., 1995),U.S. Pat. No. 5,620,290 (Homfeldt et al., 1997), and U.S. Pat. No. 6,939,097 (Carr et al., 2005), Shapes other than washers may also use these twisted type teeth, as in the clips of U.S. Pat. No. 4,406,505 (Avramovich 1983) and No. 4,961,712 (Schwenk et al., 1990).

One might consider using a washer so thick that the teeth are unable to spring back to the flat condition; however, such a piece would not easily fit in between two metal pieces and may cause the two metal pieces to deform. Also since a thick washer requires more material, it would be more expensive.

A better washer would be constructed so that the teeth are at right angles to the metal pieces to which contact should be made. Then, when the washer is tightened against the metal pieces, the teeth will not be able to spring back into the plane of the washer and will be forced to embed themselves into the adjacent piece. In embedding, both the teeth and the metal piece being contacted will deform together, resulting in a contact area where air is excluded so that the contact area will not be subject to corrosion. The height of the teeth can be designed so that the washer is guaranteed to punch through a specified thickness of anodizing. The shape and number of teeth can be designed to give a desired contact area and therefore a desired electrical resistance. The contact could be made along the inner diameter of a hole in the metal pieces; however, that might limit the amount of contact area available so it would be preferable to contact the metal pieces on an exposed face.

The washer of U.S. Pat. No. 5,828,008 (Lockwood et al., 1998) does have teeth at right angles to the piece to be contacted; however, they are only on one face. For use with machine screws, two of these washers are required. In that case, the conduction path is from the first metal piece to be connected, to the first washer, then to the machine screw, then to the second washer, then to the second metal piece to be connected. Since the conduction path has four places where current transitions between parts, there is great likelihood of a poor connection at one of the transition points and hence poor reliability. In addition, the total connection path is much longer than necessary and therefore will have relatively high resistance. A final problem is that the screw must generally be made of stainless steel to resist corrosion. The relatively poor electrical conductivity of stainless steel and the long path through the screw will limit the amount of current which can be safely conducted.

In the case of Lockwood, the washer is constructed with a concave shape. As the fastener is tightened, the washer will flatten. This change in shape will give a radial motion to the teeth which will scrape across the metal surface. For anodized surfaces the scraping may not be enough to break through the coating. It would be preferable to have the teeth directly penetrate some distance into the metal.

U.S. Pat. No. 5,435,746 (Leeb 1995) and associated U.S. Pat. No. 5,501,008 (1996) also use an electrical contact at right angles to the piece to be contacted, but it is intended for use with specialized assembly tooling and an adhesive which makes the connection permanent. In the case of application to solar modules, it is necessary to provide for module repair or replacement and a permanent connection is inappropriate.

One might consider use of the electrical grounding stud as described in U.S. Pat. No. 5,207,588 (Ladouceur et al., 1993), U.S. Pat. No. 5,441,417 (1995), and U.S. Pat. No. 5,644,830 (1997). This invention has a washer with right angle features connected to the washer and an attached stud, and also has right angle features connected to the washer and an attached rivet. The stud might be inserted through a hole in the frame of the solar module, then a nut fastened to the stud to hold it in place. The rivet could then be used to join to the mounting structure. This is clearly a cumbersome assembly process. In addition, the grounding stud will be an expensive part to fabricate and since typically four connectors are required per solar module, the total cost will be prohibitive.

Another problem with using available washers is that the washer needs to be inserted in between two metal pieces. When mounting a photovoltaic module there are four mounting holes, so one would need to carefully position four washers and then align the module to the mounting pieces. This would clearly be very difficult to do. It would be preferable to have a washer with features which retain it in position.

There are a number of available washers that have features for retaining to a bolt, such as that of U.S. Pat. No. 5,620,290 (Homfeldt et al., 1997), illustrated in FIG. 1. To use such a washer one would position four bolts through the holes in the frame of a module and place a washer on each bolt. The module would then be positioned on the mounting structure, then the module secured in place with four nuts. There are several problems here. The first is that the retaining force may not be large enough, and as the large and cumbersome module is positioned, the bolts may be knocked loose. It would be preferable to retain the washer directly to the module or mount, and then insert the bolts after the pieces have been aligned. A second problem is that the available washers are of the star type construction and do not guarantee connection as detailed previously.

There are several manufacturers who make inserts that are press fit into sheet metal parts and could thus provide the desired retention feature. For the least assembly effort, it would be desirable to construct the electrical connecting washer as an integral part of such an insert. Since the press fit process will also guarantee electrical connection, only one side of the washer would need to have the electrical connecting features.

For very high volume applications, it would be desirable to integrate the washer into the fastener and therefore eliminate assembly steps.

Accordingly, several objects and advantages of the present invention are:

-   -   1. to provide a washer which will guarantee electrical         continuity between two metal pieces after they have been         mechanically assembled even if the pieces are made of anodized         aluminum;     -   2. to provide a washer with a large surface contact area for low         electrical resistance;     -   3. to provide a washer which will be retained on one metal piece         so that a second metal piece may be aligned to the first metal         piece for mechanical assembly without disturbing the washer;     -   4. to provide a washer which requires no special tooling but         makes electrical connection during the mechanical assembly         process.     -   5. to provide a washer which can be integrated with a fastener         for minimum assembly time.

Still further objects and advantages will become apparent from a consideration of the ensuing description and drawings.

BRIEF SUMMARY OF THE INVENTION

The present invention consists of a bonding washer for maintaining electrical connection in the joining of two metal pieces, constructed with metal teeth perpendicular to the body of the washer, and may be constructed so as to fasten to one of the metal pieces before assembly.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a prior art washer with bolt retention features.

FIG. 2 shows an exploded view of an assembly with a prior art washer with bolt retention features.

FIGS. 3-8 show perpendicular teeth construction details.

FIG. 9 shows the preferred embodiment of the invention.

FIG. 10 shows the preferred embodiment of the invention inserted onto a metal piece.

FIG. 11 shows an exploded view of an assembly with the preferred embodiment.

FIGS. 12-13 show an alternative embodiment of the invention with clip feature for thin metal pieces.

FIG. 14 shows an alternative embodiment of the invention with clip feature inserted onto a thin metal piece.

FIG. 15 shows a second alternative embodiment of the invention with clip feature for thin metal pieces.

FIG. 16 shows a third alternative embodiment of the invention with finger retention feature for metal rails.

FIG. 17 shows a third alternative embodiment of the invention with finger retention feature mounted on a metal rail.

FIG. 18 shows a fourth alternative embodiment of the invention with press fit retention feature.

FIG. 19 shows a fourth alternative embodiment of the invention with press fit retention feature inserted into a metal piece.

FIG. 20 shows a fifth alternative embodiment of the invention with pin features.

FIG. 21 shows a sixth alternative embodiment of the invention with diamonds substituted for pins.

FIG. 22 shows a seventh alternative embodiment of the invention with features for electrical connections on the outside of the pieces being assembled.

FIG. 23 shows a seventh alternative embodiment of the invention with features for electrical connection on the outside of the pieces being assembled in exploded view.

FIG. 24 shows a seventh alternative embodiment of the invention with features for electrical connections on the outside of the pieces being assembled after assembly.

FIG. 25 shows an enlarged view of a seventh alternative embodiment of the invention with features for electrical connections on the outside of the pieces being assembled after assembly.

FIG. 26 shows a eighth alternative embodiment of the invention with integral threaded nut.

FIG. 27 shows a eighth alternative embodiment of the invention with integral threaded nut after assembly.

FIG. 28 shows a ninth alternative embodiment of the invention with integral rivet feature.

FIG. 29 shows a cross-sectional view of a ninth alternative embodiment of the invention with integral rivet feature.

FIG. 30 shows a ninth alternative embodiment of the invention with integral rivet feature after assembly.

FIG. 31 shows a tenth alternative embodiment of the invention with integral solar module end clamping features.

FIG. 32 shows an eleventh alternative embodiment of the invention with integral solar module midpoint clamping features.

FIG. 33 shows a twelfth alternative embodiment of the invention for use when only one metal piece has an anodized coating.

FIG. 34 shows the embodiment of FIG. 33 as it is assembled with a metal rail.

REFERENCE NUMERALS IN DRAWINGS

100—star washer body (prior art)

101—longer teeth of star washer (prior art)

102—shorter teeth of star washer (prior art)

200—screw (prior art)

201—upper metal piece (prior art)

202—star washer (prior art)

203—lower metal piece (prior art)

300—single tooth formed by triangular punch

400—four teeth formed by square punch

500—multiple teeth formed by circular punch

600—single circular tooth formed by circular punch

700—tooth formed by pin

800—tooth formed by two opposed circular teeth

900—upward-facing teeth (preferred embodiment)

901—upper washer section (preferred embodiment)

902—downward-facing teeth (referred embodiment)

903—lower washer section (preferred embodiment)

904—hinge (preferred embodiment)

905—clearance hole (preferred embodiment)

906—fingers (preferred embodiment)

1000—hole in first metal piece

1001—first metal piece

1100—bolt

1101—flat washer

1102—second metal piece

1103—hole in second metal piece

1104—flat washer

1105—split washer

1106—nut

1200—upward-facing teeth (first alternative embodiment)

1201—body (first alternative embodiment)

1202—clearance opening (first alternative embodiment)

1203—U-shaped bend (first alternative embodiment)

1204—tab (first alternative embodiment)

1301—downward-facing teeth (first alternative embodiment)

1500—upward-facing teeth (second alternative embodiment)

1501—first body section (second alternative embodiment)

1502—second set of upward-facing teeth (second alternative embodiment)

1503—second body section (second alternative embodiment)

1600—upward-facing teeth (third alternative embodiment)

1601—downward-facing teeth (third alternative embodiment)

1602—spring fingers (third alternative embodiment)

1700—metal rail

1701—side of metal rail

1702—second side of metal rail

1800—downward contacting teeth (fourth alternative embodiment)

1801—upward-facing teeth (fourth alternative embodiment)

1802—tubular section (fourth alternative embodiment)

1803—flat portion (fourth alternative embodiment)

2000—flat washer section (fifth alternative embodiment)

2001—double pointed pin (fifth alternative embodiment)

2002—hole retention feature (fifth alternative embodiment)

2100—adhesive layer (sixth alternative embodiment)

2101—diamond (sixth alternative embodiment)

2102—backing sheet (sixth alternative embodiment)

2200—flat washer section (seventh alternative embodiment)

2201—downward-facing teeth (seventh alternative embodiment)

2202—tubular body (seventh alternative embodiment)

2203—slits (seventh alternative embodiment)

2204—outward-facing teeth (seventh alternative embodiment)

2600—threaded section (eighth alternative embodiment)

2601—tubular body (eighth alternative embodiment)

2800—mandrel tail (ninth alternative embodiment)

2801—tubular body (ninth alternative embodiment)

2802—washer section (ninth alternative embodiment)

2803—slits (ninth alternative embodiment)

2804—outward-facing teeth (ninth alternative embodiment)

2805—downward-facing teeth (ninth alternative embodiment)

2900—mandrel head (ninth alternative embodiment)

2901—closed tubular end (ninth alternative embodiment)

3100—first set of teeth (tenth alternative embodiment)

3101—second set of teeth (tenth alternative embodiment)

3102—nut (tenth alternative embodiment)

3103—clearance hole (tenth alternative embodiment)

3104—captive bolt (tenth alternative embodiment)

3105—body section (tenth alternative embodiment)

3200—first set of teeth (eleventh alternative embodiment)

3201—second set of teeth (eleventh alternative embodiment)

3202—first metal piece of first solar panel (eleventh alternative embodiment)

3203—second metal piece or second solar panel (eleventh alternative embodiment)

3204—clearance hole (eleventh alternative embodiment)

3205—body section (eleventh alternative embodiment)

3300—downward-facing teeth (twelfth alternative embodiment)

3301—washer section (twelfth alternative embodiment)

3400—second metal piece (twelfth alternative embodiment)

DETAILED DESCRIPTION—FIGS. 1 Through 5—Preferred Embodiment

FIG. 1 illustrates features of the prior art. This star washer is formed from a flat metal piece. Star washer body 100 has two sets of teeth on its internal circumference. FIG. 2 illustrates the prior art in an assembly. The longer teeth 101 will retain the washer on the threads of screw 200, the shorter teeth 102 will make electrical connection to the upper metal piece 201 and lower metal piece 202 when the fastener is tightened. Teeth 102 are twisted out of the plane of the washer body 100. When screw 200 is tightened, upper metal piece 201 and lower metal piece 202 will press on the teeth 102. Since the washer is made out of a spring metal, teeth 102 will resist the tightening. As screw 200 is tightened, teeth 102 will scrape against upper metal piece 200 and lower metal piece 201. This scraping is sufficient to clear dirt or grease from a surface, but is too weak to break through an anodized surface. As screw 200 is further tightened, the teeth 102 will be forced back into the plane of the star washer body 100.

FIGS. 3-8 show several methods of constructing teeth which are perpendicular to the plane of the washer. As shown in FIGS. 3-6, one may punch out a single triangular tooth 300 with a triangular punch, or one may punch out four triangular teeth 400 with a square punch. A larger number of teeth 500 may be formed with a round shape. To simplify the forming process, a single circular tooth 600 may be made. The circular tooth has the advantage that the resulting structure is very rigid. It should be apparent to those skilled in the art that more complex shapes could also be used to form teeth. While punching is probably the simplest method of forming thin metal pieces into the desired shape, it should be apparent to those skilled in the art that other methods such as casting, machining, pressure forming, and photochemical machining could be used. The important distinction over the prior art is that the perpendicular orientation of the teeth allows for greater mechanical contact and hence greater electrical contact.

As shown in FIG. 7, pins may also be used to obtain the desired perpendicular structure instead of forming sheet metal. It should be apparent to those skilled in the art that the pins may also be hollow, for instance in a cylindrical shape, or may have an irregular shape. During assembly the opposing pin points will transmit forces directly between the two pieces to be connected and so will be the best way to ensure that the pins embed into the two pieces. The opposing points also will have a short direct path between the pieces to be connected and therefore have very low resistance; however, this may not be a cost-effective method. A more practical method may be to construct a pin-like structure as is shown in FIG. 8. Two circular teeth 800 are constructed on a sheet which is then folded so that the teeth are directly opposed. As shown in FIG. 8, the teeth have a cross-sectional height greater than their cross-sectional thickness, and, also in cross-section, are asymmetrical with respect to the perpendicular.

FIG. 9 shows the preferred embodiment of the invention. The bonding washer is formed out of a thin metal sheet. Upward-facing teeth 900 are perpendicular to upper washer section 901. Downward-facing teeth 902 are perpendicular to lower washer section 903. The teeth are formed, then the part is folded on hinge 904 so that the teeth are in direct opposition. The teeth 900 and 902 are shown with a simple smooth circular shape. It should be evident to those skilled in the art that more complicated shapes could also be used. A clearance opening in the form of a hole 905 allows a fastener to be inserted through the bonding washer. Extending downward on the inner circumference of clearance hole 905 are fingers 906.

FIG. 10 shows the preferred embodiment after it has been pushed into a hole 1000 of first metal piece 1001. Fingers 906 are constructed with a twist so that they provide a spring force to retain the bonding washer in position. The preferred embodiment is shown with four fingers. This number allows the preferred embodiment to provide retention in holes and also in slots where the slot opening is equal to the distance between adjacent fingers. It should be apparent to someone skilled in the art that other numbers of fingers could also be used.

FIG. 11 shows an exploded assembly with the preferred embodiment. Bolt 1100 is inserted through flat washer 1101, second metal piece clearance hole 1103, preferred embodiment clearance hole 905, first metal piece 1001, flat washer 1104, split washer 1105 and nut 1106. As nut 1106 is tightened, downward-facing teeth 902 will be forced into first metal piece 1001, upward-facing teeth 900 will be forced into second metal piece 1102. First metal piece 1001 and second metal piece 1102 are preferably formed of anodized aluminum. Since the downward-facing teeth 902 are perpendicular to the surface of the lower washer section 903 and the surface of the first metal piece 1001, the teeth cannot spring back but must embed into the surface of the first metal piece 1001. Similarly, the upward-facing teeth 900 will embed into the surface of the second metal piece 1102. The bonding washer is made of a material harder than that of the first metal piece 1001 and the second metal piece 1102. The bonding washer may also have a thin coating of a material such as chromium or titanium nitride in order to achieve the desired hardness. Because the upward-facing teeth 900 and the downward-facing teeth 902 are in close proximity, the electrical path from the first metal piece through the bonding washer to the second metal piece is extremely short, and therefore the connection has low electrical resistance.

The preferred embodiment is shown with a bolt and nut, but it should be apparent to one skilled in the art that other types of fasteners may be used, including through hole type fasteners such as rivets. Clamping type fasteners which are positioned outside the first and second metal pieces may also be used.

Height, cross-sectional area, and number of downward-facing teeth and upward-facing teeth can be chosen in order to achieve a desired value of electrical conductivity. These choices must be traded off against the clamping force required to force the pieces together.

Alternative Embodiments—FIGS. 12-34

FIGS. 12 and 13 show two views of an alternative embodiment of the invention, a U-shaped metal sheet featuring upward-facing teeth 1200 and downward-facing teeth 1301, perpendicular to body 1201, and an elliptical clearance opening 1202. The end of each arm of the “U” is curved into a perpendicular U-shaped bend 1203, ending in tab 1204, which forms a spring clip.

FIG. 14 shows this alternative embodiment, pushed onto the edge of second metal piece 1102. The spring clip formed by U-shaped bend 1203 and tab 1204 attaches the bonding washer to the second metal piece 1102. Tab 1204 is constructed to be outside the diameter of flat washer 1101 so that flat washer 1101 can provide even force against second metal piece 1102. Clearance opening 1202 allows a fastener to be inserted through the bonding washer. Clearance opening 1202 is somewhat elliptical in shape in order to accommodate variability in the position of hole 1103.

FIG. 15 shows a second alternative embodiment of the invention, a clip formed by a pair of parallel U-shaped plates joined by two U-shaped bends and having a first set of upward-facing teeth 1500 on first body section 1501 and a second set of upward-facing teeth 1502 on second body section 1503. When the clip is mounted on a metal piece, the second set of upward-facing teeth 1502 will contact that metal piece. After assembly, the first set of upward-facing teeth 1500 will contact a second metal piece. By using two body sections, more teeth can be accommodated and in general this will result in reduced electrical resistance through the teeth. The electrical path from the first metal piece through the clip to the second metal piece is now longer than for the first alternative embodiment, so that portion of the electrical resistance will be greater. Depending on the exact details of construction the total electrical resistance may be greater or less than for the first alternative embodiment.

A variation of this embodiment would allow the clip to be pushed on after first metal piece 1001 and second metal piece 1102 have been positioned together. In that case, the teeth would be made to contact both pieces from the outside.

FIG. 16 shows a third alternative embodiment of the invention, which takes the form of a clamp with two vertical sides, comprising spring fingers 1602, perpendicular to a flat rectangular surface 1603 bearing upward-facing teeth 1600 and downward-facing teeth 1601. FIG. 17 shows how the spring fingers grab on to the sides 1701 and 1702 of a metal rail 1700. The spring fingers retain the clamp in place on metal rail 1700 while it is assembled into a larger structure. The fastener for the third alternative embodiment will generally be of the clamping type for use in applications where clamping is appropriate, as opposed to bolting through a clearance hole.

FIGS. 18 and 19 show a fourth alternative embodiment of the invention and its application, respectively. A circular washer bears upward-facing teeth 1801. Downward contacting teeth 1800 are perpendicular to tubular section 1802. The outer diameter of the downward contacting teeth 1800 is chosen so that it can be press fit into first metal piece 1001. A tool is required which can exert sufficient pressure on flat portion 1803 in order to force the bonding washer into hole 1000, deforming the material of first metal piece 1001 around hole 1000. As a result of this press-fit operation, the bonding washer is firmly mechanically and electrically joined to first metal piece 1001, as shown in FIG. 19. The first metal piece 1001 may now be mechanically assembled into a larger structure, such that teeth 1801 will embed in the metal of the larger structure.

FIG. 20 shows a fifth alternative embodiment of the invention. Flat washer-like section 2000 has embedded pins 2001. The pins 2001 are pointed at both ends and so will embed into the two metal pieces during assembly to make electrical contact. Since conduction is only through the pins, flat washer-like section 2000 may be made of plastic. Retention feature 2002, a short cylinder attached to the washer-like section, is also made of plastic and so may readily deform when pressed into a hole. The plastic should be chosen to provide a spring action which retains the washer in the hole.

FIG. 21 shows a sixth alternative embodiment of the invention. Double-sided adhesive sheet 2100 has small industrial diamonds 2101 stuck to one side. The sheet 2100 may be peeled off backing sheet 2102, exposing adhesive on its underside. Sheet 2100 may then be stuck to a metal piece, the adhesive retaining the washer and diamonds in position. The force applied during assembly will cause the diamonds to penetrate the adhesive. The irregular shape of the diamonds will allow them to function like the pins of the fifth alternative embodiment directly conducting current from one metal piece to the other.

FIGS. 22 and 23 show a seventh alternative embodiment of the invention, in isolation and aligned with pieces to be attached, respectively. One end has a flat washer section 2200, bearing downward-facing teeth 2201, which function identically to those of the preferred embodiment. Tubular body 2202 has slits 2203 which begin a distance from washer section 2200 sufficient to accommodate the combined thickness of first metal piece 1001 and second metal piece 1102. The surfaces between slits 2203 have outward facing teeth 2204 along the first half of their length.

The seventh alternative embodiment does not have retention features. When first metal piece 1001 and second metal piece 1102 are aligned, bolt 1100 is inserted through the bonding washer unit, then bolt 1100 and the bonding washer unit together are inserted through second metal piece 1102 and first metal piece 1001. As in FIG. 11, washer 1104, split washer 1105, and nut 1106 are installed on bolt 1100. When nut 1106 is tightened, elements illustrated in FIG. 22 collapse, as tubular body 2202 folds back on itself in the vicinity of the slits 2203. (FIGS. 24 and 25 show how the outward-facing teeth 2204 will then face toward first metal piece 1001.) As nut 1106 is further tightened, downward-facing teeth 2201 embed into second metal piece 1102 and outward-facing teeth 2204 embed into first metal piece 1001, thus electrically connecting first metal piece 1001 and second metal piece 1102. Installation of the seventh alternative embodiment entails a longer electrical path between the first metal piece 1001 and second metal piece 1102 than the preferred embodiment and is therefore less desirable. It may, however, represent some cost savings in the assembly process.

FIG. 26 shows a eighth alternative embodiment similar to the seventh alternative embodiment, except that nut 1106 has been replaced by a threaded section 2600 within tubular section 2601. As shown in FIG. 27, when bolt 1100 is inserted into the threaded section and tightened, it presses against washer 1101 and deforms the bonding washer unit, making electrical connection in a similar fashion as with the seventh alternative embodiment.

FIGS. 28 and 29 show a ninth alternative embodiment similar to the seventh alternative embodiment but incorporating rivet features. Mandrel head 2900 is engaged with closed tubular end 2901. Mandrel tail 2800 protrudes through tubular body 2801 and out past washer section 2802. Assembly is illustrated in FIG. 30. The holes of two metal pieces 1001 and 1102 are aligned, and the bonding washer unit is inserted through both holes. A riveting tool is used to push down on washer section 2802 while pulling on mandrel tail 2800. The pulling force will cause tubular body 2801 to deform in the vicinity of slits 2803. Outward-facing teeth 2804 will move until they face toward first metal piece 1001, in a similar manner as shown in FIGS. 24 and 25. As additional pulling force is exerted on mandrel tail 2800, downward-facing teeth 2805 embed into second metal piece 1102, and outward-facing teeth 2804 embed into first metal piece 1001, thus electrically connecting the two metal pieces. The ninth alternative embodiment has a longer electrical path between the first metal piece 1001 and second metal piece 1102 than the preferred embodiment and therefore has greater resistance. It may, however, represent some cost savings from the assembly process.

As with normal rivets, the pulling force results in a deformation of mandrel head 2900 and closed tubular end 2901 which mechanically holds the entire assembly in place. As the pulling force is further increased, mandrel tail 2800 breaks off for a finished assembly.

FIG. 31 shows a tenth alternative implementation of the invention. This implementation incorporates a clamping function appropriate for use with a solar module and mounting rail. In use, second metal piece 1102 of solar module is positioned on metal rail 1700. First set of teeth 3100 are then positioned to contact metal rail 1700: second set of teeth 3101 are positioned to contact second metal piece 1102. Captive bolt 3104 is inserted through hole 3103 and screwed into nut 3102. As captive bolt 3104 is tightened against body section 3105, first set of teeth 3100 embed into metal rail 1700 and second set of teeth 3101 embed into second metal piece 1102, thus making electrical connection. Captive bolt 3104 is further tightened to provide sufficient clamping force between first metal piece 1001 and second metal piece 1102. This implementation may be fabricated with sheet metal or machined from an extruded blank. It should be apparent to someone skilled in the art that other fabrication techniques may also be used.

FIG. 32 shows an eleventh alternative implementation of the invention. This implementation incorporates a clamping function appropriate for use with two solar modules and a mounting rail. In use, first set of teeth 3200 are positioned to contact first metal piece 3202 of first solar module. Second set of teeth 3201 are positioned to contact second metal piece 3203 of second solar module. Bolt 3104 is captive in mounting rail 3205. Bolt 3104 is inserted through hole 3204 and screwed into nut 3102. As nut 3102 is tightened against body section 3205, first set of teeth 3200 embed into first metal piece 3202 and second set of teeth 3201 embed into second metal piece 3203, thus making electrical connection between the two solar modules. Nut 3102 is further tightened to provide sufficient clamping force between first metal piece 3202, second metal piece 3204 and metal rail 1700.

FIG. 33 shows a twelfth alternative implementation of the invention. This implementation is appropriate for use when only one of the metal pieces has an anodized coating. The bonding washer consists of a body section 3301 and one set of downward facing teeth 3300. FIG. 34 shows the twelfth alternative embodiment as it is assembled. Downward facing teeth 3300 are positioned to contact metal rail 1700. Second metal piece 3400 directly contacts washer section 3301. Second metal piece 3400 is constructed of a corrosion resistant material such as tin plated copper, zinc coated steel, or stainless steel. It should be apparent to someone skilled in the art that other suitable materials may be used. The bonding washer is also constructed out of a corrosion resistant material and therefore good electrical connection can be made just by clamping the two pieces together. As bolt 1100 and nut 1106 are tightened, downward facing teeth 3300 will forcibly embed themselves into metal rail 1700, thereby making electrical contact.

CONCLUSIONS, RAMIFICATIONS, AND SCOPE OF INVENTION

Thus the reader will see that the bonding washer of the invention provides a fastener which offers excellent electrical bonding of metal pieces used in photovoltaic and other applications. The alternative embodiments described herein make the bonding washer design adaptable to a wide range of situations, while promoting ease of assembly.

Although the description above contains many specificities, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments of this invention. Thus the scope of the invention should be determined by the appended claims and their legal equivalents, rather than by the examples given. 

What is claimed is:
 1. A bonding element for making an electrical connection between two metal pieces when the metal pieces are rigidly clamped together with at least a portion of the bonding element disposed between them, the bonding element comprising a sheet metal body member, which comprises: a first body portion and a second body portion, said body portions folded together so as to be contiguous; a first set of teeth, numbering one or more, formed on said first body portion and extending away from said body member in a first direction substantially perpendicular to said first and second body portions, each tooth of said first set having a distal edge; and a second set of teeth, numbering one or more, formed on said second body portion and extending away from said body member in a second direction substantially opposite said first direction, each tooth of said second set having a distal edge, wherein at least one tooth of said second set of teeth is substantially aligned with a tooth of said first set of teeth to define at least one pair of substantially aligned, diverging teeth, whereby, when the metal pieces are clamped together with said first and second sets of teeth between them, the distal edges of said teeth are forcibly embedded into the metal pieces to make electrical contact therewith.
 2. The bonding element of claim 1, wherein the distal edge of each tooth is substantially smooth.
 3. The bonding element of claim 2, wherein the distal edge of each tooth is substantially circular.
 4. The bonding element of claim 1, wherein the distal edge of each tooth is substantially circular.
 5. The bonding element of claim 1, wherein each pair of substantially aligned teeth are hollow.
 6. The bonding element of claim 5, wherein each pair of substantially aligned teeth define a hole through the body member.
 7. The bonding element of claim 1, wherein said first and second sets of teeth comprise plural pairs of substantially aligned, diverging teeth.
 8. A bonding washer for making an electrical connection between two metal pieces when the metal pieces are rigidly held together by a fastener with at least a portion of the bonding washer disposed between them, the bonding washer comprising a sheet metal body member, which comprises: first and second substantially congruent body portions folded together about a hinge portion so as to be contiguous and substantially coextensive; an opening in each of said body portions through which a fastener can extend, said openings being substantially coextensive and substantially aligned; a first set of teeth formed on said first body portion and extending away from said body member in a first direction substantially perpendicular to said first and second body portions, each tooth of said first set of teeth having a distal edge; and a second set of teeth formed on said second body portion and extending away from said body member in a second direction substantially opposite said first direction, each tooth of said second set of teeth having a distal edge and being substantially aligned with a respective tooth of said first set of teeth to define pairs of substantially aligned, diverging teeth, whereby, when a fastener extending through said openings is tightened with said first and second sets of teeth between the metal pieces, the distal edges of said teeth are forcibly embedded into the metal pieces to make electrical contact therewith.
 9. The bonding washer of claim 8, wherein each of said openings comprises a hole located substantially at the center of its respective body portion, and said teeth surround said holes.
 10. The bonding washer of claim 9, wherein said body portions are substantially annular.
 11. The bonding washer of claim 10, wherein the distal edge of each tooth is substantially circular.
 12. The bonding washer of claim 11, wherein the distal edge of each tooth is substantially smooth.
 13. The bonding washer of claim 12, wherein each pair of substantially aligned teeth are hollow.
 14. The bonding washer of claim 13, wherein each pair of substantially aligned teeth define a hole through the body member.
 15. The bonding washer of claim 8, wherein the distal edge of each tooth is substantially circular and smooth.
 16. The bonding washer of claim 15, wherein each pair of substantially aligned teeth define a hole through the body member.
 17. A bonding element for making an electrical connection between two metal pieces when the metal pieces are rigidly clamped together with at least a portion of the bonding element disposed between them, the bonding element comprising: a metal body having a first face and a second face, said first and second faces facing away from said body in opposite directions; a first set of teeth, numbering one or more, formed on said body and extending outwardly away from said first face substantially perpendicular to a plane of said body, each tooth of said first set having a distal edge; and a second set of teeth, numbering one or more, formed on said body and extending outwardly away from said second face substantially perpendicular to said plane of said body, each tooth of said second set having a distal edge, wherein at least one tooth of said second set of teeth is substantially aligned with a tooth of said first set of teeth to define at least one pair of substantially aligned, diverging teeth, each tooth of said pair of substantially aligned teeth having a substantially annular distal edge and a hollow interior, whereby, when the metal pieces are clamped together with said first and second sets of teeth between them, the distal edges of said teeth are forcibly embedded into the metal pieces to make electrical contact therewith.
 18. The bonding element of claim 17, wherein the distal edge of each tooth of each substantially aligned pair of teeth is substantially smooth.
 19. The bonding element of claim 18, wherein each pair of aligned teeth define a hole through said body.
 20. The bonding element of claim 19, wherein all of said teeth are substantially uniform. 